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Broadband dielectric spectroscopy from Hz up to the infrared (IR) range and temperature interval 10-300 K was carried out for xBaZrO3-(1-x)BaTiO3(BZT-x, x = 0.6, 0.7, 0.8) solid solution ceramics and compared with similar studies for x = 0, 0.2, 0.4, 1 ceramics published recently (Phys. Rev. B86, 014106 (2012)). Rather complex IR spectra without appreciable mode softening are ascribed to Last-Slater transverse optic (TO) phonon eigenvector mixing and possible two-mode mixed crystal behavior. Fitting of the complete spectral range requires a relaxation in the 100 GHz range for all the samples. Below 1 GHz another relaxation appears, which is thermally activated and obeys the same Arrhenius behavior for all the relaxor BZT samples. The frequently reported Vogel-Fulcher behavior in BZT relaxors is shown to be an artifact of the evaluation from the permittivity or loss vs. temperature dependences instead of its evaluation from loss vs. frequency maxima. The relaxation is assigned to local hopping of the off-centered Ti4+ions in the frozen BTO clusters, whose size is rather small and cannot grow on cooling. Therefore BZT is to be considered as a dipolar glass rather than relaxor ferroelectric. [ABSTRACT FROM PUBLISHER]

A set of Pb(Mg1/3Nb2/3)O3 (PMN) relaxor ceramics with different porosities (66–96% of theoretical density) was processed from the pure perovskite PMN powder by varying the sintering temperature (930–980 K) and isostatic pressure. The effective room temperature permittivity at 100 Hz varied correspondingly from ~4000 to ~15?000. We measured and fitted the room temperature infrared (IR) reflectivity of corresponding polished ceramics, from which the effective dielectric function was obtained. The results were compared with the low-frequency permittivity data and discussed using several effective medium models. The best results were obtained using the Lichtenecker model (with the exponent a ≈ 0.2), which fits quite well the IR spectra as well as the static permittivity for all the porosity values. Also the simulation using the finite element method supported the same model. It allows us to conclude that the samples show quite complex shape and topology of the pores, but all of the pores show similarity with a weak nonzero percolation (open porosity). [ABSTRACT FROM AUTHOR]

Dielectric responses of ceramics from the lead-free isovalent BaZr03-BaTi03 (BZT) system were investigated from Hz frequencies up to the infrared in a broad temperature range, 10-700 K. Pure BaZr03 is a displacive weak-incipient ferroelectric with a simple cubic perovskite structure down to low temperatures, whose dielectric response is fully determined by polar phonons, the lowest-frequency one being of the Last type, unlike BaTi03, where it is of the Slater type. BaZr0.4Ti0.6O3 is a relaxor ferroelectric whose dielectric anomaly is caused by a strong, overdamped excitation, which softens from the THz down to MHz range according to the Arrhenius law and merges into a constant-loss background at low temperatures. Such a réponse is similar to lead-containing and heterovalent relaxors, but unlike them, the lowest-frequency TOI polar phonon does not soften appreciably. In the case of BaZr0.42Ti0.3O3 we have investigated the dynamic response connected with a diffuse ferroelectric phase transition. The main dielectric anomaly is again due to similar overdamped THz-microwave excitation, which, however, softens only to the GHz range near the transition temperature and below it merges with a near-constant-loss background. The picture of polar nanoregions in BZT differs from that in heterovalent relaxors, because they are pinned to the regions of the off-centered Ti4+ ions, which are frozen in our temperature range. Therefore we assign the soft relaxations to hopping of the off-centered Ti4+ ions. This is compared with the behavior of pure BaTi03 ceramics, in which the hopping of the off-centered Ti4+ ions also substantially contributes to the phase tansition dynamics. Unlike BaTiC>3, the dynamic instability, which is responsible for the diffuse ferroelectric and relaxor behavior in BZT, is fully due to the hopping dynamics of the off-centered Ti4+ ions rather than due to soft phonons, and therefore the diffuse transition is of the order-disorder type. [ABSTRACT FROM AUTHOR]

Infrared (IR) reflectivity spectra of nominally pure Pb(Zr1-x Tix)03 ceramics with different Ti/Zr concentration (x = 0.42-0.58) were measured and evaluated, along with the time-domain terahertz transmittance spectra in the temperature range 10 K-900 K. The temperature dependence of the low-frequency vibrations, related to Pb atoms, was analyzed in terms of two overdamped modes--a soft mode and an anharmonic hopping central mode--in the cubic and high-temperature ferroelectric phase and three main vibrations in the low-temperature ferroelectric phase with the doubled unit cell: two E-symmetry modes (the soft mode and a mode corresponding to antiphase vibrations of neighboring Pb atoms in the terahertz range) and the antiferrodistortive mode producing the antiphase tilts of the oxygen octahedra. The last bare mode is not IR active, but it becomes activated by coupling with the soft mode. As predicted by theory, the intrinsic permittivity of Pb(Zr1-xTix)O3 has a maximum at the morphotropic phase boundary, although this represents just a small percentage of the total permittivity at lower frequencies. Its maximum is linked to the softening of the anharmonic vibrations of Pb ions, perpendicular to the polarization, and shifts from x = 0.48 at room temperature to x = 0.52 at 10 K. [ABSTRACT FROM AUTHOR]

We report an investigation of hexagonal Y1-xEuxMnO3 ceramics with x = 0, 0.1, and 0.2 using infrared (IR) and terahertz (THz) spectroscopies in the temperature range between 5 and 900 K. The temperature dependence of the THz permittivity reveals a kink near the antiferromagnetic (AFM) phase transition temperature TN ≈ 70 K, giving evidence of a strong spin-lattice coupling. Below TN, two absorption peaks were revealed in the THz spectra close to 43 and 73 cm-1. While the first peak corresponds to a sharp AFM resonance exhibiting softening on heating towards TN, the second one may be attributed to an impurity mode or a multiphonon absorption peak. High-temperature THz spectra measured up to 900 K reveal only small gradual increase of the permittivity in agreement with a weak phonon softening observed in the IR reflectance spectra upon heating. This corresponds to an improper ferroelectric character of the phase transition proposed from first principle calculations by Fennie and Rabe (Phys. Rev. B 72: 100103(R), 2005). [ABSTRACT FROM AUTHOR]

Infrared reflectance, terahertz transmittance, and microwave resonance measurements show that SrTiO3 films, strained by ∼1% in biaxial tension by growing them on (110) DyScO3 substrates, undergo a pronounced phonon softening near 270 K. This in-plane soft-mode drives the ferroelectric transition. The appearance of two new low-frequency modes and splitting of the high-frequency TO4 mode provide evidence of an antiferrodistortive phase below ∼180 K. [ABSTRACT FROM AUTHOR]

From the new infrared (IR) reflectivity and time-domain terahertz spectra combined with available high-frequency dielectric data above the megahertz range in a broad temperature range of 10 to 900 K, a full picture of the soft- and central-mode behavior in the classical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) is suggested. A detailed comparison is made with the recent hyper-Raman spectroscopy data [Hehlen et al., Phys. Rev. Lett. 117, 155501 (2016)] and also with other available experiments based on inelastic light and neutron scattering. It is revealed that each type of experiment provides slightly different data. The closest agreement is with the hyper-Raman data: both techniques yield the same number of soft-mode components and the same high-temperature softening towards the temperature T∗≈400K. In addition to evaluation of the IR-terahertz data using fitting with the standard factorized form of the dielectric function, we performed a successful fitting of the same data using the effective medium approach (EMA), originally based on the assumption that the mesoscopic structure of PMN consists of randomly oriented uniaxially anisotropic polar nanodomains (PNDs) with somewhat harder transverse optical polar modes in the direction along the local PND dipole [Hlinka et al., Phys. Rev. Lett. 96, 027601 (2006)]. Evaluation using Bruggeman EMA modeling has been successfully applied in the entire investigated temperature range. These results suggest that the response perpendicular to the local dipole moment, at high temperatures induced by random fields rather than PNDs, undergoes a classical softening from high temperatures with permittivity obeying the Curie-Weiss law, ɛ⊥=C/(T−Tc), where C=1.7×105K and Tc=380K, whereas the response parallel to it shows no softening. Below the Burns temperature, ∼620K, a gigahertz relaxation ascribed to flipping of the PNDs emerges from the soft-mode response, slows down, and broadens, remaining quite strong towards the cryogenic temperatures, where it can be assigned to fluctuations of the PND boundaries. [ABSTRACT FROM AUTHOR]

Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. [ABSTRACT FROM AUTHOR]

Recently predicted presence of spin-phonon coupling in the CaMnO3 is experimentally confirmed in infrared (IR), Raman and time-domain THz spectra. Most of phonon frequencies seen below 350 cm-1 exhibit significant shifts on cooling below antiferromagnetic phase transition at TN≅120 K. Moreover, several new modes activate in the IR and Raman spectra on cooling below TN. Sum of phonon contributions to static permittivity exhibits small but reliable anomaly at TN. On the other hand, the spin-phonon coupling is not manifested in temperature dependence of radio-frequency permittivity, because intrinsic permittivity is screened by extrinsic contribution from conductivity, which enhances the permittivity to giant values. [ABSTRACT FROM AUTHOR]

Compressively strained epitaxial (001 ) EuTiO3 thin films of tetragonal symmetry have been deposited on (001) (LaAlO3)0.29-(SrAli1/2Ta1/2O3)0.71 (LSAT) substrates by reactive molecular-beam epitaxy. Enhancement of the Néel temperature by I K with 0.9% compressive strain was revealed. The polar phonons of the films have been investigated as a function of temperature and magnetic field by means of infrared reflectance spectroscopy. All three in-plane polarized infrared active phonons show strongly stiffened frequencies compared to bulk EuTi03 in accordance with first-principles calculations. The phonon frequencies exhibit gradual softening on cooling, leading to an increase in static permittivity. Additional polar phonon with frequency near the TOI soft mode was detected below 150 K. This mode coupled with the TOI mode was assigned as the optical phonon from the Brillouin zone edge, which is activated in infrared spectra due to an antiferrodistortive phase transition and due to simultaneous presence of polar and/or magnetic nanoclusters. In the antiferromagnetic phase, we have observed a remarkable softening of the lowest-frequency polar phonon under an applied magnetic field, which qualitatively agrees with first-principles calculations. This demonstrates the strong spin-phonon coupling in EuTiO3, which is responsible for the pronounced dependence of its static permittivity on magnetic field in the antiferromagnetic phase. [ABSTRACT FROM AUTHOR]

The temperature dependence of the optical phonons and high-frequency microwave excitations of morphotropic Pb(Zr1-xTix)O3 (PZT) ceramics with compositions PZT 52/48 and 53/47 were studied by a broadband spectroscopy approach, using Raman, far-infrared, time-domain terahertz (THz), and microwave spectroscopies. A careful evaluation of the evolution of phonon parameters with temperature clearly revealed only two macroscopic phase transitions of intrinsic origin, driven by phonons: the ferroelectric one at high temperatures near 650 K (driven by an anharmonic soft mode at THz frequencies coupled to a weak component at higher frequencies, ω∼70cm-1) and a transition to an antiferrodistortive phase around 400 K, signaled by a new peak (ω∼60cm-1) that appeared in the infrared and Raman spectra. This peak confirmed the onset of the antiphase tilt of the oxygen octahedra and the doubling of the unit cell, as well as the splitting of the B1-E doublet in the Raman spectra. No indications of an additional phase transition were found by these techniques down to 20 K. On the other hand, dielectric measurements below the phonon frequencies showed anomalies at lower temperatures; however, they had extrinsic character and were not related to the atomic vibrations. An excitation in the gigahertz range displayed a softening towards 270 K, in agreement with a maximum in the low-frequency dielectric loss spectra. The quantitative analysis of this excitation revealed the presence of two contributions assigned to piezoelectric resonances in grains and domain wall oscillations, which, together, satisfactorily explain the dielectric anomaly below room temperature, without taking into account another transition to a lower-symmetry phase. [ABSTRACT FROM AUTHOR]

Lattice dynamics of a single crystal of lawsonite were studied over a broad range of frequencies (1 Hz to 20 THz) using impedance, THz time-domain and infrared spectroscopies. Based on polarized spectra of complex permittivity [Formula: see text] measured as a function of temperature between 10 K and 500 K, we analyzed the properties of the two known phase transitions-an antiferrodistortive one near [Formula: see text] and a ferroelectric one, occurring at [Formula: see text]. The former one is accompanied by a flat maximum in the THz-range permittivity [Formula: see text] near [Formula: see text], which is due to an overdamped polar excitation in the [Formula: see text] spectra reflecting the dynamics of water and hydroxyl groups. The strength of this mode decreases on cooling below [Formula: see text], and the mode vanishes below [Formula: see text] due to hydrogen ordering. At the pseudoproper ferroelectric phase transition, two independent anomalies in permittivity were observed. First, [Formula: see text] exhibits a peak at [Formula: see text] due to critical slowing down of a relaxation in the GHz range. Second, infrared and THz spectra revealed an optical phonon softening towards [Formula: see text] which causes a smaller but pronounced maximum in [Formula: see text]. Such anomaly, consisting in a soft mode polarized perpendicularly to the ferroelectric axis, is unusual in ferroelectrics., (© 2022. The Author(s).)

Strontium titanate-based materials with ferroelectric or relaxor-like properties have drawn vast attention as polar dielectrics for electronics and telecommunications. Here, we study the lattice dynamics in sol-gel-derived Sr 1-1.5x Bi x TiO 3 thin films with x = 0.0053 and 0.167, deposited on Al 2 O 3 substrates, using a variable-temperature far-infrared spectroscopy in a transmittance mode. Bi doping, known to induce a low-frequency dielectric relaxation in SrTiO 3 (ST) ceramics and films, due to off-centre dopant ion displacements generating electric dipoles, is shown to affect the polar phonon behaviour of thin films. We show that in weakly Bi-doped films, the low-frequency polar TO1 mode softens on cooling but less than in undoped ST. In heavily Bi-doped ST films, this mode displays no significant frequency variation with temperature from 300 to 10 K. The polar phonon behaviour of polycrystalline Bi-doped ST thin films is comparable with that of Bi-doped ST ceramics, which exhibit dielectric relaxations and harden soft-mode behaviour instead of the ferroelectric phase transition.

Broadband dielectric and AC conductivity spectra (1 Hz to 1 THz) of the superprotonic single crystal Rb 3 H(SeO 4 ) 2 (RHSe) along the c axis were studied in a wide temperature range 10 K < T < 475 K that covers the ferroelastic ( T < 453 K) and superprotonic ( T > 453 K) phases. A contribution of the interfacial electrode polarization layers was separated from the bulk electrical properties and the bulk DC conductivity was evaluated above room temperature. The phase transition to the superprotonic phase was shown to be connected with the steep but almost continuous increase in bulk DC conductivity, and with giant permittivity effects due to the enhanced bulk proton hopping and interfacial electrode polarization layers. The AC conductivity scaling analysis confirms validity of the first universality above room temperature. At low temperatures, although the conductivity was low, the frequency dependence of dielectric loss indicates no clear evidence of the nearly constant loss effect, so-called second universality. The bulk (intrinsic) dielectric properties, AC and DC conductivity of the RHSe crystal at frequencies up to 1 GHz are shown to be caused by the thermally activated proton hopping. The increase of the AC conductivity above 100 GHz could be assigned to the low-frequency wing of proton vibrational modes., (Creative Commons Attribution license.)

Core-shell composites of ferromagnetic conducting nanoparticles La 0.65 Sr 0.35 MnO 3 (LSMO) embedded in an insulating matrix of TiO 2 (LSMO@TiO 2 ) have been processed, structurally and magnetically characterized, and their DC magnetoresistivity and complex dielectric response measured and fitted from Hz up to the infrared (IR) range (10 14 Hz). XRD indicates that the TiO 2 shells are amorphous. Modelling of the IR spectra using standard models based on the effective medium approximation has it confirmed and has characterized the effective phonon modes of the LSMO nanoceramics and LSMO@TiO 2 composite. Modelling of the lower-frequency spectra has shown that TiO 2 shell thicknesses are rather non-uniform down to thin nm values, which leads to giant low-frequency permittivity values and non-negligible free-carrier tunnelling among the LSMO cores. Two main dielectric dispersion regions were observed and shown to be due to the inhomogeneous conductivity-the one occuring in the 10 11 -10 12 Hz range relates to nonmagnetic less-conducting dead layers on the surface of LSMO nanocrystallites and the broad second one below the 10 10 Hz range is due to the non-uniform thicknesses of the dielectric TiO 2 shells. In the IR range, effective phonon modes of the LSMO nanoceramics and LSMO@TiO 2 composite were characterized from the reflectivity spectra., (© 2020 IOP Publishing Ltd.)

Pb2MnTeO6, a new double perovskite, was synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction. Pb2MnTeO6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ∼120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s(2) lone-pair electrons, together with a surprising off-centering of Mn(2+) (d(5)) magnetic cations. This strong first-order phase transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below TN ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ∼150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb2MnTeO6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb2MnTeO6.

Universal dielectric response (UDR) and nearly constant loss (NCL) dispersive regimes have been investigated in fast ion conductors with perovskite and NASICON structure by using NMR and impedance spectroscopy (IS). In this study, the electrical behavior of La(0.5)Li(0.5)TiO3 (LLTO-05) perovskite and Li(1.2)Ti(1.8)Al(0.2)(PO4)3 (LTAP0-02) NASICON compounds was investigated. In both systems a three-dimensional network of conduction paths is present. In the Li-rich LLTO-05 sample, lithium and La are randomly distributed on A-sites of perovskites, but in LTAP0-02 Li and cation vacancies are preferentially disposed at M1 and M2 sites. In perovskite compounds, local motions produced inside unit cells are responsible for the large "near constant loss" regime detected at low temperatures, however, in the case of NASICON compounds, local motions not participating in long-range charge transport were not detected. In both analyzed systems long-range correlated motions are responsible for dc-conductivity values of ceramic grains near 10(-3) S cm(-1) at room temperature, indicating that low-temperature local motions, producing large NCL contribution, are not required to achieve the highest ionic conductivities.

The miniaturization and integration of frequency-agile microwave circuits--relevant to electronically tunable filters, antennas, resonators and phase shifters--with microelectronics offers tantalizing device possibilities, yet requires thin films whose dielectric constant at gigahertz frequencies can be tuned by applying a quasi-static electric field. Appropriate systems such as BaxSr1-xTiO3 have a paraelectric-ferroelectric transition just below ambient temperature, providing high tunability. Unfortunately, such films suffer significant losses arising from defects. Recognizing that progress is stymied by dielectric loss, we start with a system with exceptionally low loss--Srn+1TinO3n+1 phases--in which (SrO)2 crystallographic shear planes provide an alternative to the formation of point defects for accommodating non-stoichiometry. Here we report the experimental realization of a highly tunable ground state arising from the emergence of a local ferroelectric instability in biaxially strained Srn+1TinO3n+1 phases with n ≥ 3 at frequencies up to 125 GHz. In contrast to traditional methods of modifying ferroelectrics-doping or strain-in this unique system an increase in the separation between the (SrO)2 planes, which can be achieved by changing n, bolsters the local ferroelectric instability. This new control parameter, n, can be exploited to achieve a figure of merit at room temperature that rivals all known tunable microwave dielectrics.

Solid solutions InMn(1-x)Ga(x)O(3) (0 ≤ x ≤ 1) have been investigated using magnetic, dielectric, specific heat, differential scanning calorimetry (DSC), and high-temperature powder synchrotron X-ray diffraction (HT-SXRD) measurements. It was found that samples with 0.5 ≤ x ≤ 1 crystallize in space group P6(3)/mmc with a ~ 3.32 Å and c ~ 11.9 Å, and samples with 0.0 ≤ x ≤ 0.4 crystallize in space group P6(3)cm with a ~ 5.8 Å and c ~ 11.6 Å at room temperature. HT-SXRD data revealed the existence of a P6(3)cm-to-P6(3)/mmc phase transition at about 480 K in InMn(0.6)Ga(0.4)O(3) and at 950 K in InMn(0.7)Ga(0.3)O(3). However, no dielectric, phonon, second-harmonic-generation, or DSC anomalies were found to be associated with these phase transitions. The phase transition should be improper ferroelectric from the symmetry point of view, but the above-mentioned experimental facts, together with the absence of ferroelectric hysteresis loops, revealed no evidence for ferroelectricity in the low-temperature P6(3)cm structure. We suggest that InMn(1-x)Ga(x)O(3) corresponds to a nonferroelectric phase of hexagonal RMnO(3) with P6(3)cm symmetry. The antiferromagnetic phase-transition temperature decreases from 118 K for x = 0 to 105 K for x = 0.1 and 73 K for x = 0.2, and no long-range magnetic ordering could be found for x ≥ 0.3. Specific heat anomalies associated with short-range magnetic ordering were observed for 0.0 ≤ x ≤ 0.5. InMn(1-x)Ga(x)O(3) with small Mn contents (0.8 ≤ x ≤ 0.98) has a bright-blue color.